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Break out examples to a separate directory.
Mentioned in #52
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‎README.md‎

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DataLoader instances are created when a Request begins, and are not used once the
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Request ends.
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For example, when using with `express`:
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For example, when using with [express][]:
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```js
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function createLoaders(authToken) {
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}));
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```
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## Custom Caches
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DataLoader can optionaly be provided a custom Map instance to use as its
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## Common Back-ends
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Looking to get started with a specific back-end? Try these example loaders:
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#### Redis
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Redis is a very simple key-value store which provides the batch load method
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[MGET](http://redis.io/commands/mget). Here we build a Redis DataLoader
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using [node_redis][].
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```js
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var DataLoader = require('dataloader');
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var redis = require('redis');
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var client = redis.createClient();
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var redisLoader = new DataLoader(keys => new Promise((resolve, reject) => {
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client.mget(keys, (error, results) => {
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if (error) {
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return reject(error);
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}
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resolve(results.map((result, index) =>
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result !== null ? result : new Error(`No key: ${keys[index]}`)
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));
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});
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}));
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```
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#### CouchDB
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This example uses the [nano][] CouchDB client which offers a `fetch` method
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implementing the [HTTP Bulk Document API](http://wiki.apache.org/couchdb/HTTP_Bulk_Document_API).
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```js
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var DataLoader = require('dataloader');
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var nano = require('nano');
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var couch = nano('http://localhost:5984');
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var userDB = couch.use('users');
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var userLoader = new DataLoader(keys => new Promise((resolve, reject) => {
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userDB.fetch({ keys: keys }, (error, docs) => {
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if (error) {
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return reject(error);
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}
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resolve(docs.rows.map(row => row.error ? new Error(row.error) : row.doc));
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});
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}));
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// Usage
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var promise1 = userLoader.load('8fce1902834ac6458e9886fa7f89c0ef');
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var promise2 = userLoader.load('00a271787f89c0ef2e10e88a0c00048b');
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Promise.all([ promise1, promise2 ]).then(([ user1, user2]) => {
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console.log(user1, user2);
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});
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```
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#### SQLite
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Looking to get started with a specific back-end? Try the [loaders in the examples directory](/examples).
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SQL offers a natural batch mechanism with `SELECT * WHERE IN`. `DataLoader`
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is designed to operate over key-value stores, so in this example just requests
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the entire row at a given `id`.
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This example uses the [sqlite3][] client which offers a `parallelize` method to
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further batch queries together. Another non-caching `DataLoader` utilizes this
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method to provide a similar API. `DataLoaders` can access other `DataLoaders`.
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```js
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var DataLoader = require('dataloader');
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var sqlite3 = require('sqlite3');
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var db = new sqlite3.Database('./to/your/db.sql');
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// Dispatch a WHERE-IN query, ensuring response has rows in correct order.
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var userLoader = new DataLoader(ids => {
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var params = ids.map(id => '?' ).join();
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var query = `SELECT * FROM users WHERE id IN (${params})`;
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return queryLoader.load([query, ids]).then(
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rows => ids.map(
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id => rows.find(row => row.id === id) || new Error(`Row not found: ${id}`)
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)
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);
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});
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// Parallelize all queries, but do not cache.
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var queryLoader = new DataLoader(queries => new Promise(resolve => {
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var waitingOn = queries.length;
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var results = [];
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db.parallelize(() => {
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queries.forEach((query, index) => {
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db.all.apply(db, query.concat((error, result) => {
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results[index] = error || result;
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if (--waitingOn === 0) {
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resolve(results);
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}
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}));
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});
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});
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}), { cache: false });
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// Usage
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var promise1 = userLoader.load('1234');
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var promise2 = userLoader.load('5678');
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Promise.all([ promise1, promise2 ]).then(([ user1, user2]) => {
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console.log(user1, user2);
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});
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```
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## Video Source Code Walkthrough
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[cache algorithms]: https://en.wikipedia.org/wiki/Cache_algorithms
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[express]: http://expressjs.com/
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[babel/polyfill]: https://babeljs.io/docs/usage/polyfill/
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[node_redis]: https://github.com/NodeRedis/node_redis
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[nano]: https://github.com/dscape/nano
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[sqlite3]: https://github.com/mapbox/node-sqlite3
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‎examples/CouchDB.md‎

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# Using DataLoader with CouchDB
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CouchDB is a "NoSQL" document database which supports batch loading via the
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[HTTP Bulk Document API](http://wiki.apache.org/couchdb/HTTP_Bulk_Document_API),
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making it well suited for use with DataLoader.
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This example uses the [nano][] CouchDB client which offers a `fetch` method
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supporting the bulk document API.
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```js
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var DataLoader = require('dataloader');
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var nano = require('nano');
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var couch = nano('http://localhost:5984');
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var userDB = couch.use('users');
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var userLoader = new DataLoader(keys => new Promise((resolve, reject) => {
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userDB.fetch({ keys: keys }, (error, docs) => {
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if (error) {
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return reject(error);
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}
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resolve(docs.rows.map(row => row.error ? new Error(row.error) : row.doc));
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});
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}));
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// Usage
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var promise1 = userLoader.load('8fce1902834ac6458e9886fa7f89c0ef');
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var promise2 = userLoader.load('00a271787f89c0ef2e10e88a0c00048b');
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Promise.all([ promise1, promise2 ]).then(([ user1, user2]) => {
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console.log(user1, user2);
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});
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```
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[nano]: https://github.com/dscape/nano

‎examples/Redis.md‎

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# Using DataLoader with Redis
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Redis is a very simple key-value store which provides the batch load method
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[MGET](http://redis.io/commands/mget) which makes it very well suited for use
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with DataLoader.
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Here we build an example Redis DataLoader using [node_redis][].
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```js
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var DataLoader = require('dataloader');
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var redis = require('redis');
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var client = redis.createClient();
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var redisLoader = new DataLoader(keys => new Promise((resolve, reject) => {
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client.mget(keys, (error, results) => {
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if (error) {
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return reject(error);
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}
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resolve(results.map((result, index) =>
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result !== null ? result : new Error(`No key: ${keys[index]}`)
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));
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});
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}));
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```
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[node_redis]: https://github.com/NodeRedis/node_redis

‎examples/SQL.md‎

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# Using DataLoader with SQLite
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While not a key-value store, SQL offers a natural batch mechanism with
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`SELECT * WHERE IN` statements. While `DataLoader` is best suited for key-value
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stores, it is still suited for SQL when queries remain simple. This example
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requests the entire row at a given `id`, however your usage may differ.
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This example uses the [sqlite3][] client which offers a `parallelize` method to
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further batch queries together. Another non-caching `DataLoader` utilizes this
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method to provide a similar API. `DataLoaders` can access other `DataLoaders`.
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```js
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var DataLoader = require('dataloader');
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var sqlite3 = require('sqlite3');
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var db = new sqlite3.Database('./to/your/db.sql');
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// Dispatch a WHERE-IN query, ensuring response has rows in correct order.
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var userLoader = new DataLoader(ids => {
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var params = ids.map(id => '?' ).join();
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var query = `SELECT * FROM users WHERE id IN (${params})`;
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return queryLoader.load([query, ids]).then(
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rows => ids.map(
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id => rows.find(row => row.id === id) || new Error(`Row not found: ${id}`)
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)
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);
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});
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// Parallelize all queries, but do not cache.
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var queryLoader = new DataLoader(queries => new Promise(resolve => {
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var waitingOn = queries.length;
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var results = [];
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db.parallelize(() => {
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queries.forEach((query, index) => {
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db.all.apply(db, query.concat((error, result) => {
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results[index] = error || result;
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if (--waitingOn === 0) {
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resolve(results);
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}
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}));
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});
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});
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}), { cache: false });
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// Usage
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var promise1 = userLoader.load('1234');
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var promise2 = userLoader.load('5678');
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Promise.all([ promise1, promise2 ]).then(([ user1, user2]) => {
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console.log(user1, user2);
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});
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```
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[sqlite3]: https://github.com/mapbox/node-sqlite3

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